The present invention relates to improving storage stability and physical properties of granular detergents which are rich in nonionic surfactant.
It is most useful with nonionic surfactants which are liquid at ambient temperature, and are therefore mobile. Without a suitable structurant, the nonionic surfactant tends to leak from the powder and soak into the cardboard container which forms an unsightly stain. Although it is possible to avoid this problem by using lower levels of nonionic surfactant in the composition, or by selecting nonionic surfactants which have a higher solidification temperature, this limits the flexibility of formulation.
The use of nonionic surfactants in granular detergent applications has been widely discussed in the prior art. The following references describe various processes and compositions for making granules which comprise nonionic surfactants.
U.S. Pat. No. 3,868,336, published 25th Feb., 1975 discloses the use of a powder premix comprising perborate, tripolyphosphate, nonionic surfactant and polyvinyl alcohol. The premix is dry added to other detergent components.
GB 2 137 221, published 3rd Oct., 1984 discloses a nonionic premix which comprises dissolved polyvinyl pyrrolidone (PVP) and soil release polymer. The premix is sprayed on to an absorbant detergent carrier particle. The PVP is used as a stabiliser for the soil release polymer.
EPA 0 215 637, published on 25th Mar., 1987 discloses the use of sugars and derivatives as structurants of spray dried detergent powders. Although nonionic surfactant may be present in such powders it is incorporated at relatively low levels (1.5% -4% in examples 1 to 5). Furthermore the spray dried powder has a low bulk density (324-574 g/l).
EPA 0 513 824, published 19th Nov., 1992, describes a process for granulating nonionic detergent and the use of a surface coating agent having a particle size of less than 10 micrometers to give a powder having a high content of nonionic surfactant (10-60%) and a bulk density of 0.6 to 1.2 g/ml. The use of polymers including polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone and carboxymethyl cellulose is disclosed (page 13, lines 17-18). However, the benefits of using any of these polymers to structure or thicken the nonionic surfactant is not disclosed.
WO 92 6160, published on 16th Apr., 1992. This application describes (example 14) a granular detergent composition prepared by fine dispersion mixing in an Eirich RV02 mixer of a paste which comprises N-methyl glucose amide and nonionic surfactant in the presence of sodium carbonate and zeolite. There is no suggestion to use polymers as structuring agents.
One aspect of the present invention is a process for making granular nonionic detergent agglomerates having a bulk density of at least 650 g/l and which comprise higher levels of nonionic surfactant than those of the prior art, but do not have problems of mobile nonionic surfactants (i.e. nonionic surfactants with low solidification temperatures) leaking from the granules and soaking into the carton.
This problem is addressed by structuring the liquid nonionic surfactant before the dispersion and/or granulation process. This is done by dissolving a structuring agent which comprises a polymer in the nonionic surfactant. Preferred structuring agents are polymers, especially polymers having more than one functional hydroxyl group, especially polyvinyl alcohols, polyhydroxyacrylic acid polymers, and polymers such as polyvinyl pyrrolidone and PVNO. Also useful as components of the structuring agent are sugars and artificial sweeteners and their derivatives.
It is a further aspect of the present invention to provide a process for incorporating sticky materials into detergent granules while still maintaining desirable physical properties including free-flowing particles which have a good resistance to caking. Sticky materials if present at or close to the surface of the granules have a negative effect on flow properties. These materials also tend to gel upon contact with water which prevents effective dispensing of the granules from the dispensing drawer of a washing machine or from a dispensing device which is added to the wash with soiled load. In this aspect of the present invention these problems are overcome by using sticky materials as structuring agents of the nonionic surfactants thereby improving the surface properties of the granules.
In a further aspect of the invention, high bulk density granular detergent compositions and components are provided which comprise nonionic surfactants and structuring agents.